Primary/secondary (“P/S”) piping systems are used to isolate the pressure differential established by a pump from those established by other pumps in the same system. P/S piping allows any pump in the system to operate with virtually no tendency to induce flow, or even disturb flow, in other loops. P/S piping systems have become increasingly popular in many commercial and residential plumbing systems, such as hydronic heating and cooling systems. In such systems purge valves are essential to the operation and maintenance of the systems. Hydronic heating systems have gained popularity due to the comfortable average temperature they provide uniformity in heating. Hydronic systems use water, or water-based solutions, to move thermal energy from where it is produced to where it is needed. Thermal energy is absorbed by the water at a heat source, conveyed by the water through the distribution piping, and finally released into a heated space by a heat emitter. Because hydronic heating and cooling systems rely on the flow of water through the pipes, the presence of air bubbles or pockets within the piping can lead to inefficiency and malfunction of the system. Purge valves are used to empty the system of air upon installation and during maintenance to provide for a more efficient system. Previous systems utilized purge valves located on the secondary loop in order to remove air from the secondary loop. The use of such valves can lead to pressure differentials that can affect the operation of the remainder of the system.
Hydronic systems utilize a liquid fluid to shift energy (i.e. BTUs) from one location to another. Typically this is accomplished by heating up (or in cooling applications, cooling) a liquid, such as water, or a mixture of water and other fluids (such as glycol antifreeze) to elevate the boiling point and lower the freezing point, and pumping the liquid to another location where the captured energy in the fluid is released. The hydronic solution can be heated through the use of a boiler, solar energy, geothermal pump, or any other means. The hydronic solution can be cooled by use of a heat pump, geothermal pump, or other such means of cooling the solution.
Hydronic systems require periodic maintenance, either to replace the water in the system or to replace a mixture of water and antifreeze, to de-scaling the heat exchangers or to flush out sludge, etc. This is accomplished by draining the hydronic system, flushing with a de-scaling and/or cleaning solution, draining and filling the system back up with new fluid. Historically, purging a typical hydronic system has been accomplished by plumbing an assembly consisting of a boiler drain connected to a check valve and connected to another boiler drain. This method, while functional, is far from ideal. There are several connections as part of the assembly which each provide a potential leak path. Further, disadvantageously, the check valve typically does not provide for complete shutoff and during normal operation of the system the check valve offers some internal flow restriction.